The fist completed example in Europe for the remediation of an aquifer contaminated with chlorinated solvents by a combination of adsorption and biodegradation

The site of the New High-Speed Railway Station of Bologna is historically affcted by contamination due to low and diffse concentrations of chlorinated solvents, mainly PCE and TCE. The stratigraphic sequence is represented by alluvial deposits. An alternation of coarse-grained and fie-grained deposits characterizes the alluvial succession. In order to manage the contaminated site and with the aim of designing an effient remediation strategy, a fist phase of activity dealt with the site characterization and was addressed to better defie the hydrogeological setting and the water quality status evolution. The 3D geological/hydrogeophysical model shows a complex hydrogeological setting, typical of alluvial plains, that can be schematized into three separate aquifers. The two shallower aquifers are relevant for the contamination issue. The analysis of the variation over time of the water contaminant concentrations (from 2005 to 2018) allowed us to point out: (i) a low mean level of contamination with a decreasing trend for chlorinate solvents concentration; (ii) the presence of few “hot spots” with a contamination level still slightly above the regulatory limits. Site investigation has been integrated with a microcosm study with the presence of electron donors (lactate). Based on the results, biological reductive dechlorination was recognized as a potential approach for the site remediation but the extremely low CAHs concentration and the consequent kinetic limitation made it unfeasible for the site. The possibility to use a new dispersed colloidal activated carbon (Plumestop™, Regenesis) was experimentally investigated as a site-specifi remediation approach. The micrometric carbon with proprietary surface-charge modifiation to enable dispersion, could be easily injected in the contaminated aquifer creating an in-situ adsorption zone potentially able to quickly reduce CAHs concentration and to raise the kinetics of the biological reduction by locally increasing the bioavailable CAHs concentration at the carbon surface. The technology was co-injected with an electron donor (HRC™), to provide initial biostimulation of the treatment. We observed reduction of CAHs concentrations to non-detectable level within only few weeks from the application. The parent compounds (PCE and TCE) and daughter compound cis-DCE have shown reductions of one order of magnitude within fist month. A sequential increase of vinyl chloride has been observed in subsequent monitoring data, indicating solvent degradation to be proceeding without limitation despite the signifiant reduction in aqueous-phase contamination. Full-scale results provide information on the long-term trend of the groundwater treatment onsite. The work illustrates the remediation measures adopted and the results of post-treatment monitoring for a period of 2 years. The results that led to the procedure closure derive from the integration of multidiscilinary data, using a multiscale approach. This research represents the fist completed example in European territory for the remediation of an aquifer contaminated with chlorinated solvents by a combination of adsorption and biodegradation.